The production of elements on the sub-micron order is considered the limit with today's semiconductor technology for increasing density and integration, and some technique completely different from conventional fine processing technology (such as lithography) is needed in order to create even finer elements. It is believed that if the elements of a device could be smaller than sub-micron, then it would be possible to fabricate a quantum device (single electron tunneling device) that would control individual electrons, rather than controlling the flow of groups of electrons as in semiconductors produced up to now, and this has become an area of fervent research of late (publication 1: S. Ueda: Ovo Butsuri, 62, 889 (1993)).
The layered aluminum fine particles obtained with the present invention are single crystals of metallic aluminum whose surface is covered with an oxide insulator (alumina), and when these are placed on a substrate, it should be possible to create an electronic device based on single electron tunneling, which utilizes the passage of electrons one by one through this insulation layer (publication 2: R. Wilkins, E. Ben-Jacob, and R. C. Jaklevic: Phys. Rev. Lett., 63, 801 (1989): an example is given of single electron tunneling in metallic ultrafine particles placed on a substrate). Therefore, these layered aluminum fine particles are believed to contribute greatly to obtaining an ultrafine semiconductor intended for a single electron tunneling quantum device. Most conventional methods for manufacturing fine particles containing aluminum involved evaporation in a gas method (publication 3: Solid Physics and Metal Physics Seminars, Special Edition, "Ultrafine Particles," p. 68; "5. Generation of Ultrafine Particles,"; Agne Technology Center (1984): the generation of ultrafine particles by evaporation in a dilute gas method is discussed), but the fine particles obtained with these methods were all fine particles of alumina, and there are no cases of the production of layered aluminium fine particles that can be used for elements in a quantum device that utilizes single electron tunneling, such as are obtained with the present invention.
In view of this, in an effort to solve the above problem, the inventors used a fine particle generating device featuring magnetron sputtering to generate layered aluminum fine particles, and analyzed the particles thus generated using a transmission electron microscope (TEM) and electron beam diffraction. They also examined the dependence of particle size on the shape of the fine particle generating source, the temperature, and so on.
As a result, it was learned that when the distance from the aluminum sputtering target to the aperture attached to the distal end of the generating source is set at about 100 mm, and the aperture vicinity is cooled with liquid nitrogen, layered aluminum fine particles with a diameter of about 5 to 500 nm are generated through the aperture.
Furthermore, the inventors arrived at the present invention upon discovering that when the vicinity of the outlet from the fine particle generating source is not cooled with liquid nitrogen, layered aluminum fine particles the same as those mentioned above can be generated by shortening the distance between the aluminum sputtering target and the aperture to about 30 to 50 mm.